Black shading appears in faces
Try the following solutions


Maybe just because of the Smooth Shading applied for a low poly 3D model: Your model is currently at a low poly stage so change it into high res model or remove smooth shading until you add in more details to the model(maybe at least till you add subsurfs).
Normals Issue: Try recalculating the normals -> enter edit mode and select all then press Ctrl+N key
Duplicate Vertices or edges issue: Enter into edit mode and select all, then press W key and click on Remove doubles